AFAP-03 NATO fire effluent toxicity test method

What it is

AFAP-03, printed on its own cover as AFAP-3, is a NATO Allied Publication that defines a laboratory test method: how to burn a small specimen of a material in a tube furnace and turn the gases it releases into a single number, the TOXICITY INDEX. It is the third of a five-part AFAP series that NATO uses to screen candidate materials for fire hazard before they go into military applications: AFAP-1 sets the pre-selection policy, AFAP-2 measures smoke generation, AFAP-3 measures toxicity, AFAP-4 measures surface spread of flame, and AFAP-5 measures heat release rate. Nations record their agreement to use the series in STANAG 4602, which is the agreement that gives AFAP-3 force; read on its own it creates no obligation, and it reaches a supplier the way any Allied Publication does, "in relation to an invitation to tender or a contract in which it is incorporated."

What the test actually measures

A conditioned specimen, weighing (1.000 ± 0.050) g, is burnt for a fixed 20 minutes in a silica combustion tube at each of two temperatures: 800°C for eight gases (carbon monoxide, carbon dioxide, oxides of nitrogen, sulphur dioxide, hydrogen fluoride, hydrogen chloride, hydrogen bromide and hydrogen cyanide) and, conditionally, phenol; and 350°C for formaldehyde and acrolein. The effluent is trapped either in a 40-litre gas bag or bubbled through impinger solutions, analysed by one of a fixed set of permitted techniques per gas (FTIR and ion chromatography are the primary choices for most), and the measured concentration of each gas is scaled to what 100 g of the material would produce in 1 m3, divided by a fixed "fatal for a 30-minute exposure" concentration for that gas, and summed across every gas analysed to give the TOXICITY INDEX. Phenol, the eleventh gas, is only added to the sum if the index from the other ten comes out between 6 and 10; below or above that band it is not analysed at all.

What it deliberately does not claim

The document is careful to frame the result correctly. It "provide[s] comparisons between candidate materials, but do[es] not predict the behaviour of the materials, or combinations of materials, in actual fire conditions," and its own scope clause states the index "should not be interpreted as an assessment of toxicity hazard under actual fire conditions." It also excludes, by design, acute mental incapacitation effects, delayed or long-term toxicity, and the toxicity of particulate combustion products - the gas list is a pragmatic set chosen for a general assessment, not an exhaustive toxicology.

Two things a reader usually gets wrong

Colorimetric gas detector tubes are banned outright, and so is using elemental analysis (testing for chlorine, bromine, fluorine, nitrogen or sulphur and inferring a gas from the element) to decide whether a gas needs analysing at all - both have produced false negatives in practice. And phenol specifically cannot be collected in the gas bag: it condenses on the bag walls and understates the result, so when it is analysed it has to be by liquid injection from an impinger solution.

Apparatus and reproducibility

Because the whole point of a TOXICITY INDEX is that one laboratory's number means the same thing as another's, the document is unusually specific about the rig: combustion tube dimensions and tolerances, a thermocouple calibrated to IEC 60584-2, water of the grade set by ISO 3696, an air supply at 2 litres/minute, and a furnace whose temperature profile has to be measured against a fixed envelope on first use, after any repair, and at least once a year. Every gas is measured twice per run, and if the two determinations differ by more than a set tolerance the laboratory runs two more specimens rather than averaging the discrepancy away. An inter-laboratory round-robin already exists for two of the harder analyses, hydrogen fluoride by ion chromatography and phenol by HPLC, which is the closest the document comes to giving a reader outside confidence in a result.

The test report

The document fixes what a test report has to contain: laboratory and supplier identity, test dates, a full material and specimen description (including coatings, NATO stock numbers and any prior test history), the collection and analytical technique used for each gas with its detection limit, any gas not tested, ignition and burning observations, every intermediate value, the final TOXICITY INDEX, and the fixed caveat that "these results relate only to the behaviour of the specimens of the material under the particular conditions of test." An optional set of datasheets, cross-referenced to STANAG 4602's Materials Fire Characteristics Data Sheets, is one accepted way to record it.

Obtaining the document

AFAP-03 is published by the NATO Standardization Office and listed in the NATO Standardization Document Database, free of charge. NATO's documents are not sold by ComplyTrain and we host no copies of them.

Standards it references

• AFAP-01Background
• AFAP-02Background
• AFAP-04Background
• AFAP-05Background